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Study Of Bypass Coupling Twin-Wire Indirect Arc Welding Process And Properties Of Surfacing Layers

Posted on:2022-03-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:D T WuFull Text:PDF
GTID:1481306314457694Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
As a new high-efficiency and energy-conservation welding process,twin-wire indirect arc welding(TWIAW)was advantageous in high deposition efficiency,low heat input to workpiece,small fusion ratio and minor deformation of weldment.However,its welding process window was narrow and defects such as poor fusion at the weld toe was easily formed,which significantly restricted TWIAW engineering application.In order to improve the fusion at the weld toe,bypass coupling twin wire indirect arc welding(BC-TWIAW)technique was developed,in which the cathode wire with high heat generation and fast melting speed was connected to the workpiece.Therefore,there are two arcs in BC-TWIAW,that is,one is the indirect arc between twin wires,the other is direct arc between anode wire and workpiece.In this thesis,the arc characteristics,droplet transfer behavior and thermal field of the BC-TWIAW were comprehensively studied through experiments and numerical simulation.The welding current,arc voltage and weld formation under different process parameters were compared to reveal the influence of welding process parameters on the weld formation during BC-TWIAW.The hybrid characteristics between the twin-wire indirect arc and the bypass coupling direct arc were highlighted.Meanwhile,both the corrosion resistance mechanism and wear resistance reaction of BC-TWIAW surfacing layer were explored.Accordingly,the key problems of the narrow process window and poor fusion at weld toe for TWIAW technique can be effectively solved through utilizing the bypass coupling arc.In particular,the high deposition efficiency and low heat input to workpiece of indirect arc welding were beneficial for preparing surfacing layers with good performance.The distribution mechanism of welding current,the coupling reaction of twin wire indirect arc and bypass coupling direct arc,and droplet transfer of the twin wires were clearly captured by using high-speed camera system and the welding current/arc voltage synchronous acquisition device.The anode wire feeding speed is the main factor affecting total welding current,while cathode wire feeding speed is the main factor affecting the indirect arc current and the current distribution ratio between indirect arc and direct arc.With the increase of wire feeding speed,total welding current increases.The indirect arc current and the ratio of indirect arc current to direct arc current rise when the cathode wire feeding speed increases.Through the optimal matching of the twin wire feeding speed,twin-wire indirect arc and bypass coupling direct arc can form a composite arc with synchronous and stable combustion.Anode wire droplets spray into molten pool in the form of fine droplet,while cathode wire droplets flow into molten pool along liquid bridge.According to the arc characteristics and coupling mechanism of twin-wire indirect arc and bypass coupling direct arc obtained from process experiment,the"double elliptical+dual-ellipsoidal" hybrid heat source model for the bypass coupling twin wire indirect arc welding was established.The numerical simulation results showed that the BC-TWIAW had lower heat input to workpiece,faster heating and cooling rate of deposited metal and heat affected zone,less amount of melting base metal and narrower heat affected zone.With ER308 stainless steel wire as filling material,highly anti-corrosion surfacing layers were prepared on low carbon steel Q235 steel plate.Through the analysis of microstructure,intergranular corrosion,pitting corrosion and passive film characteristics,the solidification mode of weld pool and the cooling process of weld were discussed.Compared with the conventional MIG process,the corrosion resistance mechanism of the 18-8 series stainless steel surfacing layer was demonstrated.All the surfacing layers were mainly composed of γ austenite.However,more δ phase with finer grains were formed due to the faster cooling rate,compared to that of the MIG surfacing layer.The surfacing layer achieved a better intergranular corrosion resistance and pitting corrosion resistance.With the nickel-based super-alloy wire and iron-based wear-resistant flux cored wire as anode wire and cathode wire respectively,high temperature wear-resistant surfacing layer with high efficiency and low cost was prepared.The results showed that the matrix structure of the surfacing layer was y-Fe-Ni,accompanying with Cr-C,Nb-C and other hard phases distributed on the grain boundary.High temperature wear resistance of surfacing layers was determined by the comprehensive influence of the oxidation resistance of y-Fe-Ni matrix and the skeleton structure of Nb-C,Cr-C and other hard phases.
Keywords/Search Tags:twin-wire indirect arc welding, droplet transfer, thermal field, corrosion resistance, high temperature wear
PDF Full Text Request
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